Electron discharge device cathode



May 19, 1959' 'w. T. IIVIILLIS 2,887,507

' ELECTRON DISCHARGE DEVICE CATHODE I Filed Oct. 11. 1951 Inventor: Walter" T. MiHis,

am/O M His Attorneg.

United States Patent ELECTRON DISCHARGE DEVICE CATHODE Walter T. Millis, Owensboro, Ky., assignor to General Electric Company, a corporation of New York Application October 11, 1951, Serial No. 250,818

17 Claims. (Cl. 313-261) My invention relates to cathodes for use in electron discharge devices and, more particularly, to indirectly heated tubular cathodes.

In the art concerning electron discharge devices, one of the most desirable forms for cathodesis that of a hollow tubular member which is coated on at least a part of its outer surface with a thermionically electron emissive material and which contains within the hollow space formed thereby an electric resistance or the like for indirectly heating the tubular member to a sufiiciently high temperature at which the emissive material emits electrons. This is evidenced by the very great number of such cathodes employed in receiving tubes produced on a mass production basis. With the advance of the art, electron discharge devices, and in particular receiving discharge tubes, are becoming smaller and smaller in physical size, a large proportion of the currently produced receiving discharge devices being known as miniature and sub-miniature types. Heretofore, tubular cathodes of the form described have been made mainly of two types, the first being selected lengths or sleeves of scamless extruded or drawn metal tubing and the second being of sheet metal blanks formed in the shape of a tube or sleeve with an axially extending lock seam being effected between the adjoining edges of the formed blank.

The seamless, extruded type cathode has been found to be excellent in that it maintains its shape well under extremes of mechanical and thermal conditions and that it may be formed in very small sizes consistent with the demand for less space consumption. However, the seamless, extruded type cathode is limited bythe very impor- 1 tant disadvantage that it is much more costly to manufacture than lock seamed, metal blank cathodes, a dis advantage highly accented in the mass production of discharge devices where a fraction of a cent in the cost of each unit is of considerable significance. For this reason, the lock seamed metal blank cathodes have been the predominant type of cathode employed in the form described. It is well known to those skilled in the art, however, that the lock seamed, metal blank cathode is extremely diflicult and expensive to manufacture in the small sizes being currently required, e.g., round tubular cathodes .040" or less in diameter, especially when considered in the light of the great numbers in which such cathodes are made. Further, as the required size of vide such a cathode for use in electron discharge devices which affords a relatively large internal space therewithin for a given outer size.

Briefly stated, the cathode of my invention comprises a blank of sheet metal in tubular configuration with the adjoining edge portions of the sheet metal blank overlying one another to form an axially extending seam including only two layers of the sheet metal in superposed, preferably freely slidable, relation. One of the edge portions is recessed from the sheet metal blank and the other edge portion not only overlies the one edge portion but abuts therewith along the line of recession, thus forming a lap-butt seam. Mechanically or thermally originated peripherally compressive pressures are therefore withstood by the abutting structure of the seam. In combination with the cathode itself I may provide at least one member, preferably a wafer of sheet insulating material such as mica, having an aperture therein through which the tubular cathode extends, the size and shape of the aperture being correlated to the cross-sectional size and shape of the tubular cathode so that the cathode is constrained against mechanically or thermally originated peripherally expansive forces or pressures.

The novel features of my invention are pointed out with particularity in the appended claims. Howevenfor abetter understanding of the invention, together with further objects and advantages thereof, reference should now be had to the following description taken in conjunction with the accompanying drawing, wherein:

\Fig. l is an elevational view, in section, of an electron discharge device of a type in which the cathode of my invention is particularly advantageously employed; Fig. 2 is an elevational view of a cathode embodying the features of my invention; Fig. 3 is a cross-sectional view taken along'line 33 of Fig. 2; Fig. 4 is a cross-sectional view of a prior art type cathode; Fig. 5 is similar to Fig. 3 illustrating a modification of the cathode illustrated by Figs. 2 and 3; Fig. 6 is a cross-sectional view of a prior art 'type' cathode of rectangular cross-section; Fig. 7 is a cross-sectional view of a cathode embodying my inven tion which isrectangular in cross-section; Fig. 8 is similar to Fig. 7,1illustrating a modification of the cathode shown by Fig. 7; Fig. 9 is a cross-sectional view of another embodiment of my invention; and Fig. 10 is a cross-sectional view of still another embodiment of my invention.

Referring now to Fig. l, I have shown an electron discharge device of the type employing indirectly heated cathodes becomes smaller and smaller, the available space within a lock seamed type cathode is consumed in greater proportion by the seam itself thereby making it difiicult to position a suitable heating element therein.

Accordingly, it is a primary object of my invention to provide a new and improved cathode for use in electron And it is a still further object-of my invention to prov tubularcathodes which may advantageously be embodiments of my invention. The electron discharge device comprises an evacuated and hermetically sealed glass envelope '1 within which there is mounted a tubular cathode 2 extending through two apertures 3 and "4 in members such asyvafers 5 and 6 made of insulatingmaterial, preferably mica. In accordance with my invention, apertures 3 and 4 may be of such a sizeand shape as to constraincathode 2 from appreciably peripherally expanding, as will be further explained presently. Cathode 2 may have heads 7 extending wholly or partly around the periphery thereof so that cathode'z is also constrainedfrom moving axially within apertures3 and 4. Asuitable heating element 8 is positioned within the inner space defined by cathode 2, element 8 being energizedby electric current during the operation of the device to heat cathode, 2 sufficiently so thatit emits electrons. A control electrode or grid structure is provided by two posts, 9 and 10, which are supported between wafers 5 and 6 and which carry a plurality of spiraled turns of grid wire 11 surrounding cathode 2 as shown. A suitable anode structure includes a hollow cylinder 12 of sheet metal which has radially extending fins 13 and 14 secured to support posts 15 and 16. Posts 15 and ,tion heat transfer.

16, in turn, are supported between wafers 5 and, 6, tabs 17 on the extremities thereof preventing wafers 5 and 6 from moving away from one another. Fins 13 and 14, which-bear on the inner surfaces of wafers. 5 and; 6, prevent. Waf from m g ow d one anoth r, and at the same time aid in cooling: cylinder 12 by radia- The entire electrode structure is supported by a plurality of lead-in; prongs or connectors 18-22 which are relatively stiff and which are sealed in mutually insulated and spaced relation through the lower portion of envelope 1. External electrical connections'are made to connectors 182., the anode electrode being connected through connector 18, the control electrode through connector 22, the cathode. 2 through connector 21, and the heating element 8 through connectors 1 and 29. While two wafers 5 and 6have been illustrated in Fig. 1, it will be apparent to, those skilled in the art that only one such wafer may be required in certain other electrode structures utilizing a cathode of the type exemplified by cathode 2.

Referring next to Fig. 2, cathode 2 is illustrated more clearly to a larger scale in combination with the wafers 5 and 6. As shown in Figs. 2 and 3, cathode 2 comprises a blank 23 of sheet metal which is formed in tubular configuration with the adjoining edge portions 24 and 25 thereof superposed to provide a seam 26 having a thickness only twice the thickness of thesheet metal. As will be pointed out, the cross-sectional geometry of the cathode tube or sleeve may assume various shapes, that illustrated by Figs. 2 and 3 being circular. At least a part of the surface of cathode 2 is coated, as for instance by spraying, with a suitable electron-emissive material 27, which may be barium oxide or any other such material known to the art. The raised beads 7 may be projections stamped in the metal blank 23 or may be added, as by welding, to the surface of the blank 23. Preferably, beads 7 do not extend onto the edge portions 24 and.25 so that they do not interfere with seam 26. Since the beads 7 form no part of my invention and in some cathode constructions may not be required, they have been omitted from Figs. 3 through also, for clarity, wafers 5 and 6 and material 27 have been omitted from these figures, only the metal blank and the seam therefor being shown in cross section. While the sheet metal blank 23 from which cathode 2 is formed is most conveniently rectangular in shape before being formed into tubular configuration in order that edge portions 24 and overlie uniformly along the length of seam 26 and that the ends of the resultant tube or sleeve are square with respect to the sleeve itself, it will be apparent that a blank 23 in shape other than rectangular may be employed for special purposes. For example, a tab 28, which may be an integral part of the blank 23, may be provided in order that electrical connection and some direct support for cathode 2 is obtained by bonding a lead-in connector to the tab 28.

Turning, for the moment, to a prior art type cathode illustrated in cross section by Fig. 4, it will be seen that the prior art type cathode comprises a blank 29 of sheet metal which has edge portions 30 and 31 each bent back upon itself in a U-shaped cross section. The blank 29 is rolled or formed into a tubular configuration and the free side of each U-shaped edge portion is engaged in the bight of the other U-shaped edge portion to form a lock seam. This construction is familiar to those skilled in the art and while it is less costly than drawn seamless tube cathodes and has served satisfactorily for relatively large outer diameter cathodes, it has two important disadvantages, to wit, that it cannot easily be manufactured on a low-cost mass-production basis by automatic machinery. in sizes that are in the order of 0,040 outer diameter or less, and that in such small sizes, a relatively great proportion of the, internal, space within the tube, for a given outer diameter orsize, is taken up by the lock seam which is in thickness four times the thickness of the, sheet metal, as shown. Thus, in small size cathodes which inherently enclose a small hollow space, the situation is aggravated by the lock seam to the extent that a suitable heating element, such as element 8, will not fit easily within the cathode sleeve.

My invention overcomes these disadvantages and provides a low cost cathode, easily manufactured in extremely small sizes by automatic machinery, which, for a given outer dimension or diameter, has a relatively large enclosed space for receiving a heating element. Consider again, now, Fig. 3 and notice that the superposed edge portions 24 and 25 form a seam 26 no greater in thickness than twice the thickness of the metal sheet. Further, in accordance with my invention, one of the edge portions 24 and 25 (edge portion 25, as illustrated) is recessed from the metal blank 23 along a line of recession 32 which extends the entire length of the seam 26, while the other edge portion (edge portion 24) abuts with the one. edge portion at the line of recession 32. With edge portion 24 overlying or lapping edge portion 25 and abutting edge portion 25 at the line of recession 32, seam 26 is appropriately defined as a lapbutt seam.

This, cathode construction has several advantages in that the metal blank 23v may be easily and economically manufactured by automatic machinery simply by recessing one edgev portion, as by a stamping action, and then wrapping the blank 23 on a mandrel to the proper tubular or closed cross-sectional configuration, even in small sizes of 0.040" or less outer diameter. As stated previously, for a given small outer dimension or diametena relatively large proportion of the enclosed space is available for receiving a heating element since the lap-butt seam 26 is not thicker than twice the thickness of the metal sheet. Further, the abutting of the two edge portions 24 and 25, even though they are slidableupon one another and not welded or otherwise fastened, prevents the seam 26 from slipping when the cathode tube is subjected to minor peripherally contractive forces. In combination with one or more apertured members, such as wafers 5 and 6, the seam 26 is also constrained from slipping when the cathode tube is subjected to peripherally expansive forces, so that even though the lap-butt seam is simpler and more conveniently formed than the lock seam, it is entirely satisfactory from a structural viewpoint.

Referringnext to Fig. 5, I have shown a modification of the cathode illustrated by Fig. 3 which is similar to Fig. 3 except that edge portion 24 is also recessed from blank 23v along a linev of recession 33 but in the opposite direction to the recession of edge portion 25. Thus, the two recessed edge portions 24, and 25. overlap, with each abutting the other at its line of recession. The resultant seam 34 is therefore defined as a double lap-butt seam and is preferred in applications where relatively great mechanically or thermally originated peripherally com.- pressive forces are to be withstood.

It isqsometimes desirable to employ an indirectly heated tubular cathode which provides a somewhat directive stream of emitted electrons therefrom and to this end, tubular cathodes which are rectangular in CI'OSSrS6CtlOII are constructed with one or more of the outer major faces coated with emissive material. A common prior art type of sucha rectangular cross-sectional cathodc,,illustrated' by;Fig. 6, is constructed from a blank 35 of sheet metal which is formed in the tubular shape shown. The two adjoining edge portions 36 and 37- of the blank 35 constitute a, lock seam similar to that shown in Fig. 4, each edge portion being bent back upon itself in a U -shaped cross, section. The free end of each U-shapcd edge portion is engaged in the bight of the other edge portionsothat a lockseam is formed along one side of the tubular cathode, This prior art construcution is limited for-the reasons previously. set forth, namely, that it cannot be easily and economically manufactured in small sizes, ,and, thatthe lock seam is inthickness four times as great as the thickness of the sheet metal so that for a given outer dimension, the enclosed space for receiving a heating element is by proportion considerably decreased.

A rectangular cross-section embodiment of the cathode of my invention is illustrated by Fig. 7 and comprises a blank 38 of sheet metal formed to define a tubular sleeve of rectangular cross-section. A lap-butt seam is formed at one side 37 of the sleeve, and at a portion of the two sides 39 and 40 adjacent side 37, by two edge portions 41 and 42 superposed as shown. Edge portion 41 is recessed from blank 38 along a line of recession 43, as shown, while the other edge portion 42 abuts edge portion 41 at its line of recession 43. Peripherally compressive forces in a direction parallel to the plane of sides 39 and 40, i.e.,. horizontal as shown, are withstood by the edge portions in this abutt ing relation, while such forces in a transverse direction are withstood by the foot of edge portion 41 which bears upon the inner surface of side 40. Again, this cathode embodiment in combination with an apertured member, such as waters and 6, having an aperture substantially the same size and shape as the crosssection of the cathode, is constrained against peripherally expansive forces so that the lap-butt seam remains Secured under any normally adverse physical conditions. It will be apparent from the foregoing that this lap-butt seamed rectangular sleeve cathode is simple and economical to manufacture and that it encloses a larger space, for a given outer dimension, than the prior artcathode shown by Fig. 6. d

A desirable modification of the cathode of 7 is illustrated by Fig. 8, wherein an axially extending groove 44 is defined along the line of recession 43 and thefree edge of edge portion 42 is crimped or bent to reside in the groove 44. This provides all the advantages previously described and at the same time conveniently secures the edge portion 42 against peripherally ex pansive forces.

The embodiment of the cathode of my invention shown by Fig. 9 is similar to that shown by Fig. 3, except that the cathode tube or sleeve is made oval in cross-section. The seam 26 is formed as described by reference to Fig. 3 and possesses the advantageous features pointed out in connection therewith. By the oval shape shown in Fig. 9, directive emission may be obtained from one orboth of the relatively flat external surface areas. It will be obvious that a double lap-butt seam, such as seam 34, may be employed with this oval cross-section cathodeif it is desired.

Still another embodiment of my invention is illustrated by which shows a cathode comprising a. blank .45 of sheet metal formedto define a tube of a polygonal cro.ss-section having, as illustrated, major sides 46 and 47 and minor sides 48-51. A lap-butt seam is formed including adjoining edge portions 52 and 53 which are slidably superposed on the two adjacent sides 48 and,49 ofthe polygonal tube. The innermost edge portion 53 abuts the inner surface of a third side, i.e., side 47,, to provide resistance to peripherally compressive forces. Incombinat ion with an apertured member, such as wafers 5 and 6, having an aperture correlated to the size-and shape of the tube, the cathode tube by being inserted through the aperture is constrained from peripheral expansion. This embodiment, as illustrated, is particularly easilyfab ricated and is suited to provide directive emission frorn'o ne or both of the external surfaces of sides 46and 47. i

1 While the present invention has been described, referenee to particular embodiments thereof, it will be understood that numerous modifications may be made by those skilled in the art without actually departing from the invention. I, therefore, aim in the appended claims to cover all such equivalent variations as come within the true spirit and scope of the foregoing disclosure.

What I claim as new and desire to secure by Letters liatent of -the United Statesis;

1.-- For use in electron dischargedevices, the combination of a cathode comprising a single blank of sheet metal in tubular configuration and a slidable lap-butt seam of only a double thickness of said sheet metal between the adjoining edge portions of said blank, said cathode having a cross-sectional dimension of less than .041 of an inch, and at least one insulating member having an aperture therein substantially the same in size and shape as the cross-section of said cathode, said cathode extending through said aperture with said adjoining edges of said blank retained in overlapping abutting relation against radial expansive forces of said blank b said insulating member. I i

2. For use in electron discharge devices, the combination of a cathode sleeve comprising a substantially rectangular single blank of sheet metal having a crosssectionof closed configuration and a slidable lap-butt seam of only a double thickness of said sheet metal at the adjoining edges of said blank, said sleeve having a cross-sectional dimension of approximately .040 of an inch, and two insulating members each having an aperture therein essentially the same size and shape as the cross-section of said cathode, said members being positioned each on one end'of said cathode sleeve with said "sleeve extending through said apertures to retain the adjoining edges in overlapping abutting relation against radial expansive forces of said blank.

3:. The combination of a cathode comprising a single blank of sheet metal defining a tubular configuration with two edge portions of said blank slidably superposed and providing a seam of only a double thickness of said sheet metal, one of said edge portions being recessed from said blank, and the other of said edge portions overlying said'one edge portion and abutting therewith at the line of recession, said cathode having a cross-sectional dimension of approximately .040 of an inch; and two wafer members of sheet insulating material each having an aperture therein substantially the same size and shape as the cross-section of said cathode when said edge portions are abutting; said wafer members each being positioned on an opposite end of said cathode with said cathode extending through said apertures, whereby said cathode is constrained from radial expansion and contraction at said seam by said wafer members and said abutment of said edge portions, respectively.

4., For use in electron discharge devices the combination of acathode comprising a single substantially rectangular blank of sheet metal defining a sleeve of circular cross-section, a seam of only a double thickness of said sheet metal including the circumferentially adjoining edge portions of said blank slidably superposed, one of said edge portions being recessed from said blank and the other of said edge portions abutting said one edge portion at its line of recession, said sleeve having a diameter, of less than .041 of an inch; and at least one member of insulating material having a circular aperture therein correlated to the size of the cross-section of said sleeve when said edge portions are abutting; saidca'thode sleeve being inserted in said aperture.

5. For use in electron discharge devices the combination of a cathode comprising a single blank of sheet metal formed-in tubular configuration with two edge portions of said blank slidably superposed and providing a seam of only a double thickness of said sheet metal, eachof said edge portions being recessed from said blank in an opposite direction and abutting the other edge portion at the line of its recession, said cathode having a cross-sectional dimension of less than .041 of an inch; and at least one member of insulating. ma,- terial having an aperture'therein correlated in size and shape to'the cross-section of said cathode when said edge portions are abuttingj'said cathode being inserted in said aperture. 7

6'. For use in electron discharge devices, a cathode comprising a single blank of sheet metal. defining a tubular configuration with two edge portions of said blank slidably superposed and providing a lap-butt seam there between having a thickness not greater than twice the thickness of said sheet metal, said cathode having a cross-sectional dimension of less than .041 of an inch, and one of said edge portions being offset and providing a stop, said stop being abutted by the other of said edge portions.

7. For use in electron discharge devices, a cathode comprising a single blank of sheet metal defining, a sleeve of tubular cross-section and having a cross-sectional dimension of approximately .040 of an inch, and a seam for said sleeve constituted of only a double layer of said sheet metal formed by the superposition of two opposite edge portions of said blank, one of said edge portions being recessed from said blank, and the other of said edge portions slidably overlying said one edge portion and abutting therewith at the line of recession.

8. For use in electron discharge devices, a cathode comprising a single blank of sheet metal formed in tubular configuration with two edge portions of said blank slidably superposed and providing a seam of only a double thickness of said sheet metal, said cathode. having a cross-sectional dimension of less than .041 of an inch, each of said edge portions being recessed from said blank in an opposite direction and abutting the other edge portion at the line of its recession.

9. For use in electron discharge devices, a cathode comprising a single blank of sheet metal having opposite edge portions recessed from said, blank in respectively opposite directions, said blank defining a tubular sleeve having a closed cross-section with a cross-sectional dimension of the order of .040 of an inch, said edge portions being slidably superposed and providing a seam of only a double thickness of said'sheet metal and each of said edge portions abutting the other at the line of recession, whereby said tubular sleeve is restrained from radial contraction at said slidably superposed edge portions.

10. For use in electron discharge devices, a' miniature-type cathode comprising a single substantially rectangular blank of sheetv metal defining a sleeve of rectangular cross-section, an axially extending scam including two edge portions of said blank slidably superposed at one side of said rectangular cross-section sleeve and at a portion of the two sides adjacent said one side, one of said edge portions being recessed from said blank and the other of said edge portions abutting said one edge portion at the line of recession thereof.

11. A cathode as set forth in claim 10 wherein an axially extending groove is defined at the line of recession of said one edge portion and the edge of said other edge portion is bent and resides in said groove, whereby the corresponding portions between said groove and the edge of said one edge portion constitute the slidably superposed edge portions of said seam.

12. A cathode substantially as set forth in claim 7 wherein the tubular cross-section of said sleeve is oval in shape.

13. For use in electron discharge devices, a miniature-type cathode comprising a single blank of sheet metal defining a tube having a polygonal cross-section, a seam including the peripherally adjoining edge portions of said blank slidably superposed on two adjacent sides of said polygonal cross-section tube, the edge of the innermost ofsaid edge portions abutting the inner surface of a third side of said polygonal cross-sectional tube.

14'. For use in an electric'discharge device, a cathode comprising a substantially rectangular single blank of sheet metal formed in tubular configuration, said cathode having an outer diametrical dimension of the orderof .040 inch, the lateral edge portions of said blank being slidably superposed to provide a lap seam of only a double thickness of said sheet metal, at least one of said edge portions being recessed from said blank and providing a shoulder, and the other of said edge portions abutting said shoulder whereby said cathode is reinforced against collapsing during handling and radial contraction during operation in said discharge device.

15. For use in an electric discharge device, a cathode comprising a substantially rectangular single blank of sheet metal formed in tubular configuration, said cathode having an outer diametrical dimension of the order of .040 inch, the lateral edge portions of said blank being slidably superposed and providing a lap seam of only a double thickness of said sheet metal, at least one of said edge portions being recessed from said blank and thereby providing a shoulder, the other of said edge portions abutting said shoulder whereby said cathode is reinforced against collapsing during handling and radial contraction during operation in said discharge device, and an insulating. member having an aperture therein substantially the same in size and shape as the cross-section of said cathode when said other edge portion is abutting said shoulder, said cathode extending through said aperture, said insulating member being the sole means effective for maintaining said edge portions in overlapping relation with said other edge portion abutting said shoulder during operation of said discharge device.

16. For use in an electric discharge device, a cathode comprising a substantially rectangular single blank of sheet vmetal formed in cylindrical configuration, said cathode having an outer diameter of the order of .040 inch, the lateral edge portions of said blank being slidably superposed and providing a lap seam of only a double thickness of said sheet metal, the inner one of said edge portions being recessed from said blank and providing a shoulder, and the outer one of said edge portions abutting said shoulder, whereby said cathode is reinforced against collapsingduring handling and contraction during operation in said discharge device.

17. For use in an electric discharge device, a cathode comprising a substantially rectangular single blank of sheet metal formed in cylindrical configuration, said cathode having an outer diameter of the order of .040 inch, the lateral edge portions of said blank being slidably superposed and providing a lap seam of only a double thickness of said sheet metal, the inner one of said edge portions being recessed from said blank and providing a shoulder, the outer one of said edge portions abutting said shoulder, whereby said cathode is reinforced against collapsing during handling and contraction during operation in said discharge device, and an insulating member having a circular aperture therein of the same size as the outer diameter of said cathode when said outer one of said edge portions is abutting said shoulder, said cathode extending through said member, said member being the sole means effective for maintaining said edge portions in overlapping relation with said outer one of said edge portions abutting said shoulder during operation of said discharge device.

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